The International Code of Zoological Nomenclature (ICZN) is the regulatory framework containing principles universally accepted by the scientific community for managing nominal taxa and resolving any nomenclatural disputes. The Code governs the use of nominal taxa down to the subspecies level.
Note: It is important to distinguish between a nominal taxon (a published, scientifically recognized name referring to a real group of organisms) and a biological taxon (the real group of organisms).
A nominal taxon is considered available when it is published in accordance with the ICZN rules; otherwise, it is treated as a nomen nudum. For amateur naming of infrasubspecific variants, which are not regulated by the Code, formal ICZN compliance is not required.
When describing a new taxon, the correct combination of genus + species (optionally including a subgenus) constitutes the basionym. Furthermore, a representative specimen must be designated as the holotype and deposited in a public institution, becoming a permanent reference point. Additional specimens cited in the publication may be designated as paratypes.
Historically, when such designation was not mandatory, nominal taxa could be represented by syntypes (original specimens), type figures, bibliographic references, or simply by the description itself. The absence of type specimens has sometimes complicated the interpretation of the author’s intentions, generating nomina nuda (lacking elements useful for definition) or nomina dubia (uncertain, e.g., referring to specimens belonging to different species).
To ensure nomenclatural stability, one of the syntypes may be selected as a lectotype, while the remaining specimens become paralectotypes (serving the function of holotype and paratypes, respectively). In particular cases, for example to preserve a well-established name, a neotype may be designated as the official reference.
The type locality (locus typicus), including any bathymetric or stratigraphic data, corresponds to that of the holotype. If the holotype does not coincide with the locality indicated in the original publication, the specimen’s locality prevails.
In cases with multiple syntypes from different localities, all localities hold value, but to avoid ambiguity, it is advisable to designate a lectotype. Indicating the locus typicus is now mandatory for new taxa; in the past, many descriptions lacked it or contained erroneous information.
The use of subsequent designation to assign a type locality to taxa originally unlocalized has generated various inconsistencies and is currently discouraged, as it is not binding under the ICZN Code.
For any further information or details regarding the rules of nomenclature applied in zoology, please refer to the International Code of Zoological Nomenclature.